HCI 특론 (2007 Fall)

User TestingUser Testing

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Hall of Fame or Hall of Shame?

• frys.com

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Hall of Shame

• Does not follow OBVIOUS LINKS (K10) pattern

• Navigation separate from content– no links on right

• Why is this about Fry’s ISP? – I’m looking for a

store!

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Hall of Fame or Hall of Shame?

• HFS Husky Card Account Page

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Hall of Fame or Hall of Shame?

• HFS Husky Card Account Page

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Hall of Shame

• HFS Husky Card Account Page– violates

PREVENTING ERRORS (K12)

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Hall of Fame or Shame?

• The page you get if you get it wrong

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Hall of Shame

• The page you get if you get it wrong– what is

Blackboard Academic Suite?

– where am I?– is this really the

UW site?– violates SITE

BRANDING (E1)

– what is the error?– violates

MEANINGFUL ERROR MESSAGES (K13)

HCI 특론 (2007 Fall)

User TestingUser Testing

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Outline

• Why do user testing?

• Choosing participants

• Designing the test

• Collecting data

• Analyzing the data

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■ Why do User Testing?

• Can’t tell how good UI is until?– people use it!

• Other methods are based on evaluators who– may know too much– may not know enough (about

tasks, etc.)

• Hard to predict what real users will do

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■ Choosing Participants• Representative of target users– job-specific vocab / knowledge– tasks

• Approximate if needed– system intended for doctors?

• get medical students– system intended for engineers?

• get engineering students

• Use incentives to get participants

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Ethical Considerations

• Sometimes tests can be distressing– users have left in tears

• You have a responsibility to alleviate– make voluntary with informed consent– avoid pressure to participate– let them know they can stop at any time– stress that you are testing the system, not them– make collected data as anonymous as possible

• Often must get human subjects approval

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User Test Proposal

• A report that contains– objective– description of system being testing– task environment & materials– participants– methodology– tasks– test measures

• Get approved & then reuse for final report• Seems tedious, but writing this will help

“debug” your test

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Selecting Tasks

• Should reflect what real tasks will be like• Tasks from analysis & design can be used–may need to shorten if• they take too long• require background that test user won’t have

• Try not to train unless that will happen in real deployment

• Avoid bending tasks in direction of what your design best supports

• Don’t choose tasks that are too fragmented– e.g., phone-in bank test

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■ Deciding on Data to Collect

• Two types of data– process data• observations of what users are doing & thinking

– bottom-line data• summary of what happened (time, errors, success)• i.e., the dependent variables

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Which Type of Data to Collect?

• Focus on process data first– gives good overview of where problems are

• Bottom-line doesn’t tell you where to fix– just says: “too slow”, “too many errors”, etc.

• Hard to get reliable bottom-line results– need many users for statistical significance

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The “Thinking Aloud” Method

• Need to know what users are thinking, not just what they are doing

• Ask users to talk while performing tasks– tell us what they are thinking– tell us what they are trying to do– tell us questions that arise as they work– tell us things they read

• Make a recording or take good notes– make sure you can tell what they were doing

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Thinking Aloud (cont.)

• Prompt the user to keep talking– “tell me what you are thinking”

• Only help on things you have pre-decided– keep track of anything you do give help on

• Recording– use a digital watch/clock– take notes, plus if possible

• record audio & video (or even event logs)

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Video of a Test Sessionhttp://www.maskery.ca/testvideo/webdemo1.htmlhttp://www.maskery.ca/testvideo/webdemo3.html

http://dmc-av.ej1042.umn.edu/usability.ram

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■ Using the Test Results

• Summarize the data–make a list of all critical incidents (CI)• positive & negative

– include references back to original data– try to judge why each difficulty occurred

• What does data tell you?– UI work the way you thought it would?• users take approaches you expected?

– something missing?

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Using the Results (cont.)

• Update task analysis & rethink design – rate severity & ease of fixing CIs– fix both severe problems & make the easy fixes

• Will thinking aloud give the right answers?– not always– if you ask a question, people will always give an

answer, even it is has nothing to do with facts• panty hose example

– try to avoid specific questions

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Measuring Bottom-Line Usability

• Situations in which numbers are useful– time requirements for task completion– successful task completion– compare two designs on speed or # of errors

• Ease of measurement– time is easy to record– error or successful completion is harder

• define in advance what these mean

• Do not combine with thinking-aloud. Why?– talking can affect speed & accuracy

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Analyzing the Numbers

• Example: trying to get task time <=30 min. – test gives: 20, 15, 40, 90, 10, 5– mean (average) = 30– median (middle) = 17.5– looks good!

• Wrong answer, not certain of anything!• Factors contributing to our uncertainty?

– small number of test users (n = 6)– results are very variable (standard deviation = 32)

• std. dev. measures dispersal from the mean

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Analyzing the Numbers (cont.)

• This is what statistics is for• Crank through the procedures and you find– 95% certain that typical value is between 5 & 55

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Analyzing the Numbers (cont.)

Participant # Time (minutes)1 202 153 404 905 106 5

number of participants 6mean 30.0median 17.5std dev 31.8

standard error of the mean = stddev / sqrt (#samples) 13.0

typical values will be mean +/- 2*standard error --> 4 to 56!

what is plausible? = confidence (alpha=5%, stddev, sample size) 25.4 --> 95% confident between 5 & 56

Web Usability Test Results

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Analyzing the Numbers (cont.)

• This is what statistics is for• Crank through the procedures and you find– 95% certain that typical value is between 5 & 55

• Usability test data is quite variable– need lots to get good estimates of typical values– 4 times as many tests will only narrow range by 2x

• breadth of range depends on sqrt of # of test users

– this is when online methods become useful• easy to test w/ large numbers of users

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■ Measuring User Preference• How much users like or dislike the system– can ask them to rate on a scale of 1 to 10– or have them choose among statements• “best UI I’ve ever…”, “better than average”…

– hard to be sure what data will mean• novelty of UI, feelings, not realistic setting …

• If many give you low ratings -> trouble• Can get some useful data by asking– what they liked, disliked, where they had

trouble, best part, worst part, etc. (redundant questions are OK)

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Comparing Two Alternatives• Between groups experiment– two groups of test users– each group uses only 1 of the systems

• Within groups experiment– one group of test users

• each person uses both systems• can’t use the same tasks or order (learning)

– best for low-level interaction techniques

• Between groups requires many more participants than within groups

• See if differences are statistically significant– assumes normal distribution & same std. dev.

BA

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Experimental Details

• Order of tasks– choose one simple order (simple -> complex)

• unless doing within groups experiment

• Training – depends on how real system will be used

• What if someone doesn’t finish– assign very large time & large # of errors or remove & note

• Pilot study– helps you fix problems with the study– do 2, first with colleagues, then with real users

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Instructions to Participants

• Describe the purpose of the evaluation– “I’m testing the product; I’m not testing you”

• Tell them they can quit at any time• Demonstrate the equipment• Explain how to think aloud• Explain that you will not provide help• Describe the task– give written instructions, one task at a time

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Details (cont.)

• Keeping variability down– recruit test users with similar background– brief users to bring them to common level– perform the test the same way every time

• don’t help some more than others (plan in advance)– make instructions clear

• Debriefing test users– often don’t remember, so demonstrate or show video

segments– ask for comments on specific features

• show them screen (online or on paper)

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Reporting the Results

• Report what you did & what happened

• Images & graphs help people get it!

• Video clips can be quite convincing

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Summary

• User testing is important, but takes time/effort• Early testing can be done on mock-ups (low-fi)• Use ????? tasks & ????? participants

– real tasks & representative participants• Be ethical & treat your participants well• Want to know what people are doing & why, so?

– collect process data• Using bottom line data requires ???? to get

statistically reliable results– more participants

• Difference between between & within groups?– between groups: everyone participates in one condition– within groups: everyone participates in multiple conditions